Collections are similar to Dropbox or Google Drive folders, or messaging groups — but instead of files or messages, they're for Stories.
You can invite friends to participate in a Collection. That means they can contribute, view and comment on all stories in the Collection.
You can also make someone a Co-Owner of the Collection. They'll have virtually all the same privileges as you.
See the separate story under this Collections Tag to view the different privileges between Owner, Co-Owner and Participant.
You can also send a link to others to participate in a Collection. You can send it by email, text, social media or even carrier pigeon.
If your friend signs up for an account via this link, they'll automatically be connected to you and be part of the Collection.